There is a potential difference inside and outside of a cell in a normal plant and electromotive force is generated. It is possible to describe a mechanism which generates such electromotive force based on, for example, an electrophysiological model of an axial organ of a higher plant.
In particular, various methods are suggested in which a state of a root of the plant (for example, water stress) is examined non-destructively utilizing electromotive force between the root and soil.
As a prior technique in which water stress in a plant is measured utilizing the method described above, for example, Patent Document 1 is known. In Patent Document 1, connecting a first nonpolarizable electrode to the plant, connecting a second nonpolarizable electrode to soil in which the plant is planted, providing a potentiometer between the two nonpolarizable electrodes, and being able to measure water stress which is received by the plant by measuring electromotive force between both nonpolarizable electrodes using the potentiometer.
In order to accurately evaluate a time-transition of the amount of applied water stress in the leaf of the plant, it is important that specification of an initial shape of the leaf of the plant that is a measurement target is a criterion, and the water content of the leaf is observed based on the specified shape. In farmers cultivating the plant (for example, vegetables such as tomatoes), in order to improve the value of tomato (that is, the unit price), for example, it is conceivable to improve the sugar content of tomatoes. Here, the kind of irrigation to be performed and the timing of the irrigation for increasing the sugar content is mainly attributable to artificial arrangements such as farmer's past experience and intuition.
In general, increasing the sugar content of fruits such as tomatoes leads to an improvement in quality and a rise in unit prices, but has a strong aspect that since growing such fruits is not easy, yield is decreased and thereby the production amount is also decreased. In other words, there is a trade-off relationship between high performance of fruits and the yield. For this reason, in the future, it is expected to increase the productivity by improving the yield.
An object of the present disclosure is to quantitatively and time-serially suggest a change of a water content contained in a plant and accurately capture the change of the water content from an initial stage with respect to the extent of water stress applied to the plant.